U.S. Pat. Nos. 3,208,415 and 3,385,244 are illustrative of prior art machines that comprise: a work station that includes an operating instrumentality actuable to perform work on succesive workpiece assemblies that are each formed of a workpiece mount having a workpiece detachably secured thereto; and shifting means so constructed as to be actuable to shift a workpiece assembly in a prone plane on a prescribed path past the work station while operating instrumentality is actuated to perform a pattern of work on the workpiece that corresponds to said prescribed path. In these types of machines, an individual workpiece assembly must be attached to the shifting means and then removed from the shifting means before the succeeding workpiece assembly can be attached to and then removed from the shifting means. This causes a delay in the presentation of succesive workpiece assemblies to the machine, particularly when an operator is servicing a plurality of the machines.